It is known that a hot-melt adhesive is used for bonding metal and plastics together. It is also known that a hot-melt adhesive is applied to a heat-recoverable article, for example, heat-recoverable sleeve or terminal cap for covering the splices and terminals of power cables, communications cables, copper pipes, and steel pipes.
The hot-melt adhesive now in use for heat-recoverable articles adheres to not all kinds of metals and synthetic resins used for purposes such as splices and terminals, such as iron, copper, lead, aluminum, stainless steel, steel, polyethylene, polypropylene, polyvinyl chloride, polyester, chloroprene, and ethylenepropylene rubber. Some hot-melt adhesives adhere to polyethylene and metals, but do not adhere to polyvinyl chloride and polyester. Some other hot-melt adhesives adhere to polyvinyl chloride and polyester, but do not adhere to polyethylene and polypropylene.
It is known that the bonding of a polyolefin resin such as polyethylene, polypropylene, and ethylenepropylene rubber and a metal such as copper, iron, and aluminum can be achieved with ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-glycidyl methacrylate copolymer, ethylene-glycidyl methacrylate-vinyl acetate terpolymer, ionomer resin, or ethylene-acrylic acid-acrylate ester terpolymer obtained by hydrolyzing or thermally decomposing ethylene-acrylate ester copolymer. However, these polymers are not satisfactory in adhesion to lead-coated cables or polyvinylchloride sheath cables. Moreover, ethylenic adhesives are superior in low-temperature impact resistance but are poor in shear bond strength and peel strength at high temperatures. They often cause such troubles as displacing of the bonded part and leaking of a gas during use.
On the other hand, it is known that polyamide resins and saturated polyester resins are used for bonding polyvinyl chloride or polyester resin to a metal such as copper, lead, and aluminum. However, they do not adhere to polyethylene sheath cables. In addition, they are poor in low-temperature impact resistance, and the bonded parts often break or peel when the cable is bent or subjected to impact at low temperatures.
The splices and terminals of power cables and communications cables are made up of a variety of materials, and therefore it is inconvenient that the adherends are limited as mentioned above.
Recently, wires and cables and copper and steel pipes have come to be used over a broad temperature range from an extremely low temperature such as about -50.degree. C. to an extremely high temperature such as about 90.degree. C. As a result, there has arisen a demand for heat-recoverable articles coated with an adhesive which resists such a severe temperature condition. However, heretofore, a satisfied adhesive has not been obtained.
In order to solve this problem, there was proposed in Japanese Laid-Open Patent No. 123823/1981 a heat-recoverable article having an adhesive layer composed of a polyethylene adhesive and a polyamide adhesive. This heat-recoverable article adheres to a variety of adherends, but is not satisfactory in both performances at a low temperature and a high temperature.